LACP basically provides link protection / monitoring functionality to LAG. Suppose if we have configured LAG on one side and on other side no LAG is configured , in this situation LAG on our side status will be up, this may cause to communication break down if other side single link becomes not functional. To avoid such situation LACP is used , when LACP is enabled on aggregated link , it will only goes to up state when both sides exchanges LACP PDUs on LAG. Now coming to LACP mode, it can be active or passive, but for LAG to be functional at least one side must be configured with active (by default when configured LACP its mode is passive). Active member sends LACP PDUs to passive member ever one second and passive member also responds by sending PDUs. Now if both members are in active mode then they both will actively transmit LACP PDUs and other side will respond. View the attachment for guidelines about LACP and LAG monitoring and trouble shooting.
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Kashif Nawaz
JNCIP-Sec, JNCIS-Ent,JNCIS-Sec,JNCIA-JUNOS